This invention is an improvement over U.S. Pat. Nos. 4,093,294 and 4,185,865. U.S. Pat. No. 4,093,294 discloses a releasable wireline spear which penetrates a fish in order to lift it. U.S. Pat. No. 4,185,865 discloses a releasable wireline overshot which includes a split collet lifting device.
It frequently happens in oil field work that a tool or some other piece of equipment must be retrieved from an oil well after being detached, either intentionally or inadvertently. The object to be retrieved could be a downhole tool or a piece of tubing or pipe. These would all commonly be referred to as "fish" during the retrieval operation. Many of the tools have a fishing collar at the top to facilitate retrieval. A broken or detached piece of tubing, however, would not.
Most tools in use to retrieve such fish are called "overshots" and they suffer from several disadvantages. The disadvantages generally appear when it is necessary to release a fish after attaching to it, but prior to pulling it out of the well. This can be necessary, for instance, when the fish is lodged in the casing or open hole and cannot be pulled free without overloading the wireline, tubing, coiled tubing, or drill pipe, or the hoisting equipment. The fish must then be released in order to get the overshot out of the well so that other retrieval methods can be attempted.
Releasing a fish from known overshots usually requires heavy jarring or the imparting of some rotational action. Rotational action can only be imparted if the overshot is attached to a tubing or drill pipe string instead of coiled tubing or a wireline. This is a distinct disadvantage because use of a tubing or drill pipe string requires a derrick, whereas a wireline or coiled tubing operation does not. A heavy jarring action can also cause damage to the fish, especially if it is delicate, such as in the case with most survey instruments. Known overshots which can be operated on a wireline without releasing via a heavy jarring action are not generally suited for retrieving a wide variety of fish. They may only be suitable for retrieving a fish having a fishing collar such as in U.S. Pat. No. 4,004,835, or neck, or they may be suited only for retrieving a limited range of fish diameters. Finally, they may be limited in the range of weights they are capable of supporting.
It is highly desirable to have an overshot which can operate on a wireline or coiled tubing or on a drill pipe or tubing string, engaging and releasing without rotation, which can retrieve heavy fish, and which can attach to fish with or without fishing collars and fish having a wide range of diameters. An overshot having these advantages can significantly reduce the number of different sizes and styles of overshots that must be available at a drilling or workover site.